System and method for raially expanding a tubular element comprising an emergency blow-out preventer

ABSTRACT

The invention provides a system for lining a wellbore, and a method for using said system. The system comprises: a drill string ( 20 ) for drilling the wellbore; an expandable tubular element ( 4 ) enclosing the drill string, wherein a lower end portion of a wall of the expandable tubular element is bent ( 14 ) radially outward and in axially reverse direction to define an expanded tubular section ( 10 ) extending around an unexpanded tubular section ( 8 ); a pushing device ( 50 ) for pushing the unexpanded section into the expanded tubular section; a blow-out preventer ( 302 ) for closing off the wellbore in case of an emergency. Herein the blow-out preventer encloses the unexpanded tubular section and comprises a cutter ( 320 ) for cutting the unexpanded tubular section and at least one closure device ( 324 ) for closing the wellbore.

The present invention relates to a system for radially expanding atubular element. The invention also relates to a method of using saidsystem.

The technology of radially expanding tubular elements finds increasingapplication in the industry of oil and gas production from subterraneanformations. Wellbores are generally provided with one or more casings orliners to provide stability to the wellbore wall, and/or to providezonal isolation between different earth formation layers. The terms“casing” and “liner” refer to tubular elements for supporting andstabilising the wellbore wall. Typically, a casing extends from surfaceinto the wellbore and a liner extends from a certain depth further intothe wellbore. However, in the present context, the terms “casing” and“liner” are used interchangeably and without such intended distinction.

In conventional wellbore construction, several casings are set atdifferent depth intervals, and in a nested arrangement. Herein, eachsubsequent casing is lowered through the previous casing and thereforehas a smaller diameter than the previous casing. As a result, thecross-sectional area of the wellbore that is available for oil and gasproduction decreases with depth.

To alleviate this drawback, it is possible to radially expand one ormore tubular elements at a desired depth in the wellbore, for example toform an expanded casing, expanded liner, or a clad against an existingcasing or liner. Also, it has been proposed to radially expand eachsubsequent casing to substantially the same diameter as the previouscasing to form a monodiameter wellbore. It is thus achieved that theavailable diameter of the wellbore remains substantially constant along(a section of) its depth as opposed to the conventional nestedarrangement.

WO-2008/006841 discloses a wellbore system for radially expanding atubular element in a wellbore. The wall of the tubular element isinduced to bend radially outward and in axially reverse direction so asto form an expanded section extending around an unexpanded section ofthe tubular element. The length of the expanded tubular section isincreased by moving, for instance by forcing or pushing, the unexpandedsection into the expanded section. Herein the expanded section retainsthe expanded tubular shape. At its top end, the unexpanded section can,for instance, be extended by adding pipe sections or by unreeling,folding and welding a sheet of material into a tubular shape.

The present invention aims to improve the above referenced prior artsystem.

The present invention therefore provides a system for lining a wellbore,the system comprising:

-   -   a drill string for drilling the wellbore;    -   an expandable tubular element enclosing the drill string,        wherein a lower end portion of the wall of the expandable        tubular element is bent radially outward and in axially reverse        direction to define an expanded tubular section extending around        an unexpanded tubular section;    -   a pushing device for axially extending the expanded tubular        section by forcing the unexpanded section to move relative to        the expanded tubular section;    -   a blow-out preventer device (BOP) for closing an annular opening        between the expandable tubular element and the drill string.

By moving the unexpanded tubular section downward relative to theexpanded tubular section, the tubular element is effectively turnedinside out. The tubular element is progressively expanded without anexpander that is pushed, pulled or pumped through the tubular element.The expanded tubular section can form a casing or liner in the wellbore.The expanded tubular liner may have a collapse resistance which isadequate to stabilize or support the wellbore wall.

The BOP seals the opening at the upper end of the unexpanded tubularsection, thus allowing fluid, such as drilling fluid, within the systemto be pressurised. The BOP enables the drill string and/or sections ofthe expandable tubular liner to be disconnected safely, while ensuringthat well control operations can be carried out in case of a kick orblow-out. Herein, a blow-out may indicate an uncontrolled flow of(reservoir) fluids into the wellbore, which may sometimescatastrophically rise to the surface. Said fluids may include saltwater, oil, gas or a mixture of these. Blowouts may occur in all typesof exploration and production operations, not just during drillingoperations.

Preferably, the sealing capability of the BOP can withstand pressuresthat may be experienced during well control operations. The BOP is forinstance designed to withstand pressures that may be expected in case ofa blowout, for instance a maximum pressure in the range of 200 bar toabout 1600 bar or more, for instance about 400 bar to 800 bar or more.

It is preferred that the wall of the tubular element includes a materialthat is plastically deformed during expansion. The expanded tubularsection will retain an expanded shape due to the plastic deformation,i.e. permanent deformation, of the wall of the expandable tubularelement. There is no need to apply an external force or pressure tomaintain the expanded tubular section in its expanded form. If, forexample, the expanded tubular section engages the wellbore wall, noadditional radial force or pressure needs to be exerted to keep theexpanded tubular section against the wellbore wall.

The wall of the tubular element may comprise a metal such as steel orany other ductile metal capable of being plastically deformed byeversion of the tubular element. The expanded tubular section preferablyhas adequate collapse resistance to support or stabilize the wellborewall. Depending on the respective formation, the collapse resistance ofthe expanded tubular section may exceed, for example, 100 bar, 150 bar,or about 1500 bar or more.

Suitably the bending zone is induced to move in axial direction relativeto the remaining tubular section by inducing the remaining tubularsection to move in axial direction relative to the expanded tubularsection. For example, the expanded tubular section is axially fixed atsome location, while the unexpanded tubular section is moved in axialdirection through the expanded tubular section to induce said bending ofthe wall.

In order to induce said movement of the remaining tubular section, theremaining tubular section is subjected to an axially compressive forceacting to induces said movement. The axially compressive forcepreferably results at least partly from the weight of the remainingtubular section. A pushing device may supplement the weight of theunexpanded tubular section by applying an additional external force tothe remaining tubular section to induce said movement. The additionalforce applied by the pushing device may be upward or downward. Forinstance, as the length and hence the weight of the unexpanded tubularsection increases, an upward force may need to be applied to theunexpanded tubular section to maintain the total force applied to theunexpanded section within a predetermined range. Maintaining the totalforce within said range will prevent uncontrolled bending or buckling ofthe bending zone.

If the bending zone is located at a lower end of the tubular element,whereby the remaining tubular section is axially shortened at a lowerend thereof due to said movement of the bending zone, it is preferredthat the remaining tubular section is axially extended at an upper endthereof in correspondence with said axial shortening at the lower endthereof. The remaining tubular section gradually shortens at its lowerend due to continued reverse bending of the wall. Therefore, byextending the remaining tubular section at its upper end to compensatefor shortening at its lower end, the process of reverse bending the wallcan be continued until a desired length of the expanded tubular sectionis reached. The remaining tubular section can be extended at its upperend, for example, by connecting a tubular portion to the upper end inany suitable manner such as by welding. Alternatively, the remainingtubular section can be provided as a coiled tubing which is unreeledfrom a reel and subsequently inserted into the wellbore.

Optionally the bending zone can be heated to promote bending of thetubular wall.

The invention will be described hereinafter in more detail and by way ofexample with reference to the accompanying drawings in which:

FIG. 1 shows a vertical cross section of a lower portion of a system forradially expanding a tubular element;

FIG. 2 shows a vertical cross section of an example of an upper portionof the system of FIG. 1;

FIG. 3 shows a vertical cross section of another example of an upperportion of the system of FIG. 1;

FIG. 4 shows a vertical cross section of an embodiment of the system ofthe present invention;

FIG. 5 shows a vertical cross section of another embodiment of thesystem of the present invention;

FIG. 6A shows a vertical cross section of an embodiment of the presentinvention in a first state of use;

FIG. 6B shows a plan sectional view of the system of FIG. 6A along theline B-B;

FIG. 6C shows a plan sectional view of the system of FIG. 6A along theline C-C;

FIG. 7A shows a vertical cross section of an embodiment of the presentinvention in a second state of use;

FIG. 7B shows a plan sectional view of the system of FIG. 7A along theline B-B;

FIG. 7C shows a plan sectional view of the system of FIG. 7A along theline C-C;

FIG. 8A shows a vertical cross section of an embodiment of the presentinvention in a third state of use;

FIG. 8B shows a plan sectional view of the system of FIG. 8A along theline B-B; and

FIG. 8C shows a plan sectional view of the system of FIG. 8A along theline C-C.

In the drawings and the description, like reference numerals relate tolike components.

FIG. 1 shows a wellbore 1 formed in an earth formation 2. A radiallyexpandable tubular element 4, for instance an expandable steel liner,extends from surface 6 down into the wellbore 1. The tubular element 4comprises an unexpanded tubular section 8 and a radially expandedtubular section 10. The unexpanded section 8 extends within the expandedsection 10. Preferably, an outer diameter of the expanded tubularsection 10 is substantially equal to the diameter of the wellbore 1.

Although the wellbore shown in FIG. 1 extends vertically into theformation 2, the present invention is equally suitable for any otherwellbore. For instance, the wellbore 1 may extend at least partially inhorizontal direction. Herein below, upper end of the wellbore refers tothe end at surface 6, and lower end refers to the end down hole.

At its lower end, the wall of the unexpanded section 8 bends radiallyoutward and in axially reverse (in FIG. 1 the upward) direction so as toform a curved lower section 12, defining a bending zone 14 of thetubular element 4. The curved section 12 is U-shaped in cross-sectionand interconnects the unexpanded section 8 and the expanded section 10.

A drill string 20 may extend from surface through the unexpanded linersection 8 to the lower end of the wellbore 1. The lower end of the drillstring 20 is provided with a drill bit 22. The drill bit comprises, forinstance, a pilot bit 24 having an outer diameter which is slightlysmaller than the internal diameter of the unexpanded liner section 8,and a reamer section 26 having an outer diameter adapted to drill thewellbore 1 to its nominal diameter. The reamer section 26 may beradially retractable to a smaller outer diameter, allowing it to passthrough the unexpanded liner section 8, so that the drill bit 22 can beretrieved through the unexpanded liner section 8 to surface. The drillstring 20 may comprise multiple drill pipe sections 28. The pipesections 28 may be mutually connected at respective ends by male andfemale threaded connections 30. An annular space 32 between the drillstring 20 and the unexpanded tubular section 8 is referred to as thedrilling annulus 32.

The connections 30 are not shown in detail, but comprise for instancethreaded, pin and box type connections. The connections 30 may comprisejoints fabricated with male threads on each end, wherein short-lengthcoupling members (not shown) with female threads are used to join theindividual joints of drill string together, or joints with male threadson one end and female threads on the other. Said threaded connectionsmay comprise connections which are standardized by the AmericanPetroleum Institute (API).

FIG. 1 also shows a rig floor 40, which is elevated with respect to thesurface 6 and encloses an upper end of the drill string 20 and of theunexpanded tubular section 8. The rig floor 40 is part of a drillingrig, which is however not shown in its entirety. A pipe pusher 42, whichis for instance arranged below the rig floor, encloses the unexpandedsection 8. The pipe pusher is for instance supported by base frame 44.The base frame 44 provides stability, and may for instance be connectedto the drilling rig or be supported at surface 6. The pipe pusher maycomprise one or more motors 46, which are arranged on the base frame,and one or more conveyer belts 48 which can be driven by the respectivemotors. Each conveyer belt 48 engages the outside of the unexpandedsection 8. The conveyer belts 48 can exert force to said unexpandedsection 8 to force the unexpanded section to move into the expandedsection 10. Other embodiments of the pipe pusher 42 are conceivable,which will be able to exert downward or upward force to the unexpandedsection.

A sealing device 50 can be connected to the upper end of the expandedliner section 10 to seal the unexpanded liner section 8 relative to theexpanded liner section 10. Herein, the sealing device 50 enables theunexpanded liner section 8 to slide in axial direction relative to thesealing device 50. The sealing device comprises a conduit 52 which isconnected to a pump (not shown) for pumping fluid into or out of a blindannulus 44, i.e. the annular space between the unexpanded liner section8 and the expanded liner section 10. The annular space 44 is referred toas blind annulus as it is closed at the downhole end by the bending zone14. The sealing device includes one, two or more annular seals 56, 58.The seals 56, 58 engage the outside of the unexpanded section 8 andprevent said fluid to exit the blind annulus. Preferably, the sealingdevice 50 comprises at least two seals 56, 58 to provide at least oneadditional seal to improve safety and reliability in case the first sealmay fail.

The sealing device 50 can be regarded as a blind annulus blow outpreventer (BABOP). Therefore, the seals 56, 58, the connection of thedevice 50 to the upper end of expanded section 10, and one or morevalves (not shown) for closing conduit 52 will all be designed to atleast withstand fluid pressures that may arise in a well controlsituation. Depending on specifics of the formation, the sealing device50 is for instance designed to withstand pressures that may be expectedin case of a blowout, for instance in the range of 200 bar to 1600 bar,for instance about 400 bar to 800 bar or more. Such pressures may forinstance arise in the blind annulus 44 in case of a failure, forinstance due to rupture, of the expandable tubular 4 in combination witha well control situation.

The expanded liner section 10 is axially fixed, by any suitable fixationmeans, to prevent axial movement. The expanded liner section 10 may befixated at its upper end at surface. For instance, said upper end of theexpanded section may be connected to a ring or flange 59, for instanceby welding and/or screwing. Said ring can be attached to or incorporatedin any suitable structure at surface, such as the sealing device 50. Theinner diameter of said ring may be larger than the outer diameter of theexpanded section. Optionally, the expanded section 10 may be fixed tothe wellbore wall 12, for instance by virtue of frictional forcesbetween the expanded liner section 10 and the wellbore wall 12 as aresult of the expansion process. Alternatively, or in addition, theexpanded liner section 10 can be anchored, for instance to the wellborewall, by any suitable anchoring means.

At the interface indicated by the line II-II, the lower portion of thesystem shown in FIG. 1 can be connected to an upper portion as forinstance shown in FIGS. 2 and 3.

FIG. 2 shows a top drive 60 connected to an upper end connection part62, which is rotatable with respect to the top drive. Preferably, theupper end connection part comprises a flush pipe, having a smooth outersurface. The pipe end 64, which is remote from the top drive, isprovided with a threaded connection 30 as described above. The threadedend 64 is connected to an additional drill string section 66. Typically,the additional drill string section 66 will be substantially equal tothe drill string sections 28, shown in FIG. 1. At the interfaceindicated by line I-I, the additional drill pipe section 66 can beconnected to the upper end of the drill string 20 shown in FIG. 1.

A drilling annulus sealing device 70 may cover the top end of thedrilling annulus 32. The sealing device 70 comprises a housing 72, whichencloses the connection part 62 and provides an internal space 74. Atthe top end, near the top drive 60, the housing comprises one, two ormore seals 76, 78, which engage the outside of the pipe 62. Preferably,the seals 76, 78 enable the housing to slide along the pipe 62. At theopposite end, the housing may comprise one, two or more seals 80, 82which engage the outside of an additional expandable pipe section 84. Inaddition to the seals, the housing may comprise grippers 106, which mayengage the outside and/or the inside of the pipe section 84. Anactivation line 88 is connected to the housing for activating orreleasing the seals 80, 82 and/or the grippers 86. A fluid conduit 90 isconnected to the internal space 74 for supply or drainage of (drilling)fluid to or from the annular space 32.

The sealing device 70 may comprise an extending part or stinger 100. Thestinger extends into the inside of the additional expandable pipesection 84. The stinger may comprise seals 102, 104 and/or grippers 106to engage the upper end of the pipe section 84. The stinger may alsocomprise seals 108 to engage a lower end of the pipe section 84, andseals 110 to engage the inside of the upper end of the unexpandedtubular section 8 (shown in FIG. 1). A backing gas tool 192 may beintegrated in the stinger between the seals 108, 110. The backing gastool covers the inner interface between the additional expandable pipesection 84 and the unexpanded tubular section 8.

The stinger may be at least slightly longer than the pipe section 84 sothat the stinger may extend into the unexpanded section 8, which willenable the stinger to function as an alignment tool for aligning thepipe section 84 and the unexpanded section 8.

In practice, the length of the pipe section 84 may be in the range ofabout 5-20 metres, for instance 10 metres. The stinger will for instancebe about 2% to 10% longer, for instance 5% longer than the pipe section84. An annular space 112 is provided between the stinger and the pipe 62to provide a fluid connection from the annulus 32 to the space 74 andthe conduit 90.

The sealing device 70 may be referred to as drilling annulus blow outpreventer (DABOP) 70. The seals 76-82, the grippers 86, and one or morevalves (not shown) for closing conduits 88 and 90 will all be designedto at least withstand fluid pressures that may arise in a well controlsituation. Depending on specifics of the formation and the expectedmaximum pore pressures, the DABOP 70 is for instance designed towithstand pressures in the range of about 200 bar to 800 bar or more,for instance about 400 bar.

The DABOP may comprise any number of seals. The DABOP 70 may compriseone seal 76 and one seal 80, or a plurality of seals. In a practicalembodiment, two seals 76, 78 to seal with respect to the pipe 62 and twoseals to seal with respect to the tubular section 84 will provide abalance between for instance fail-safety and reliability on one hand andcosts on the other hand. For instance, the double barrier provided bythe inner seals 102, 104, engaging the inside of the expandable pipe 84,and the outer seals 80, 82, engaging the outside of the expandable pipe84, improves the reliability and leak-tightness of the sealing device70.

FIG. 3 shows an upper portion of the system of FIG. 1. The unexpandedliner section 8 is at its upper end formed from a (metal) sheet 130wound on a reel 132. The metal sheet 130 has opposite edges 133, 134.After unreeling from the reel 132, the metal sheet 130 is bent into atubular shape and the edges 133, 134 are interconnected, for instance bywelding, to form the unexpanded tubular section 8. Consequently, theexpandable tubular element 4 may comprise a longitudinal weld 135.

A fluid conduit 136 extends from the interior of the unexpanded tubularsection 8, to above the upper end of the unexpanded tubular section 8.The fluid conduit 136 may at its lower end be connected to, orintegrally formed with, a tube 138 located in the unexpanded tubularsection 8. A first annular seal 140 seals the tube 138 relative to theunexpanded liner section 8, and a second annular seal 142 seals the tube138 relative to the drill string 20. The fluid conduit 136 is in fluidcommunication with the interior space of the tube 38 via an opening 144provided in the wall of the tube 138. Furthermore the tube 138 isprovided with gripper means 146 allowing upward sliding, and preventingdownward sliding, of the tube 138 relative to the unexpanded linersection 8. The first annular seal 140 allows upward sliding of the tube138 relative to the unexpanded liner section 8.

The upper portion shown in FIG. 3 can be combined with a lower portionshown in FIG. 1, wherein the unexpanded tubular section 8 is howevercontinuously formed around the drill string 20. Herein, some of thefeatures shown in FIG. 1 are omitted in FIG. 3 to improve the clarity ofthe latter figure, such as the sealing device 50, the pipe pusher 42 anddrilling floor 40.

FIG. 4 shows the system 300 for radially expanding the expandabletubular element 4 by eversion thereof. As an example, the system 300includes the upper section shown in FIG. 2, but the system may likewiseinclude an upper section comparable to the upper section shown in FIG.3.

The system 300 includes an emergency blow-out preventer 302 for blockingthe drilling annulus in case of an emergency, such as an otherwiseuncontrollable blow-out of the well. The emergency blow-out preventercomprises a housing 304 which encloses at least a part of the unexpandedtubular section 8. The housing is preferably located at surface toenable workers access to the device, but may also be located downhole orat the seabed in case of an offshore application.

The housing 304 may be attached to the sealing device 50. Herein, thesealing device 50 may function as a wellhead. Wellhead herein means thesurface termination of the wellbore that may incorporate a means ofhanging the production tubing and installing a Christmas tree andsurface flow-control facilities in preparation for the production phaseof the well.

Optionally, and as shown in FIGS. 4 and 5, the housing 304 comprisesmultiple housing parts 306, 308, 310. Each housing part may comprise adifferent device or provide a different functionality. Respectivehousing parts are for instance cylindrically shaped, comprising flanges312 at opposite ends. Adjacent housing parts can be mutually connectedby connecting their respective flanges to each other, for instance bybolt-nut assemblies 314. The inside of each housing part may optionallybe provided with upper and lower seals 316, 318 respectively, whereineach seal is adapted to be able to engage the unexpanded liner section8. Each seal 316, 318 may include one, two or more seals, depending onlocal conditions, expected pressures, etc. The seals 316, 318 are forinstance comparable with, or similar to the seals 56, 58 of the sealingdevice or wellhead 50.

In an embodiment, shown in FIG. 4, the emergency blow-out preventer 302comprises a cutter 320. The cutter is located in a lower part of thehousing 304, for instance in first housing part 306. In addition theemergency blow-out preventer 302 comprises one or more ram-typepreventers 322, 324 for closing off the annulus 32, which are arrangedabove the cutter 320. The ram type preventers for instance include apipe ram 322 and a shear ram 324. The pipe ram can comprise two oppositeram blocks 226 which can close around the drill string 20. The shear ramcan comprise two opposite shear ram blocks 228 which can cut through thedrill string. The housing 304 may include one, two or more of each ramtype preventer, to improve reliability and fail-safety.

In another embodiment, shown in FIG. 5, the emergency blow-out preventer302 comprises a cutter 320. An annular preventer 330 is arranged abovethe cutter. The annular preventer comprises for instance one or moreinflatable packer elements 332 that can close around the drill string20. The packer elements can be inflated with pressurized fluid. Theemergency blow-out preventer 302 also comprises the shear ram 324.

A fluid conduit or kill line 334 connects the drilling annulus 32 belowthe lowest ram type preventer with an external pump system (not shown).Fluid, typically mud or heavy drilling fluid, can be circulated via thedrill string and the drilling annulus 32, indicated by arrows 336 and338 respectively, and through the kill line 334, or vice versa.

The ram type preventers are devices that can be used to quickly seal thetop of the wellbore in the event of a well control event, also known asa kick. The ram type preventer may comprise two halves of a cover forthe well that are split down the middle. Said halves can be driven byhydraulic cylinders (not shown), which are normally retracted (FIG. 6Ashows the ram blocks in their retracted position) and can force the twohalves of the cover together in the middle to seal the wellbore (asshown in FIGS. 4 and 5). These covers are for instance constructed ofsteel for strength and may be fitted with elastomer components on thesealing surfaces. The halves of the covers, also called ram blocks, mayhave a variety of configurations.

In case of the pipe ram 322, the ram blocks 326 may have a circularcutout 340 in the middle that corresponds to the diameter of the pipe inthe wellbore, for instance enabling them to seal around the drill pipe20 (see FIG. 6C). Variable-bore rams (not shown) and inflatable packers332 are designed to seal a wider range of pipe diameters. Shear ramblocks 328 are fitted with a cutting surface to enable the ram blocks tocompletely shear through the drill pipe 20 (as schematically shown inFIGS. 4 and 5), hang the drill string off on the ram blocks themselvesand seal the wellbore. Shearing the drill string limits future optionsand is employed only as a last resort to regain pressure control of thewellbore.

The various ram blocks can be changed in the ram type preventers,enabling an operator to optimize the configuration of the emergencyblow-out preventer 302 for the particular wellbore section or operationin progress.

In an exemplary embodiment, the cutter 320 comprises a guide ring 342for enclosing the unexpanded section 8 and a cutting wheel 344 (FIG. 6A)which can rotate along said guide ring around the unexpanded tubularsection. The cutting wheel herein can be moved from a first positionwherein the cutting wheel is radially retracted (FIG. 6B) to a secondposition (FIG. 7B) wherein the cutting wheel touches the outside of theunexpanded tubular section 8.

In other embodiments, the cutter 320 may comprise a laser cutter and/ora blade which can be mounted on the guide ring 342. Other options mayinclude a pressurized water cutter or a cutting rope which can engagethe outer surface of the pipe.

Typically, and as shown in FIG. 6A, the emergency blow-out preventer 302is placed above the sealing device 50 or similar wellhead device. Theemergency blow-out preventer 302 is adapted to cut the unexpandedtubular section 8 and to subsequently seal the drilling annulus 32. Inan inactive position (FIG. 6A), the cutter does not engage theunexpanded tubular section 8 (FIG. 6B) and all the ram blocks, such asram blocks 326 shown in FIG. 6C, are in a retracted position.

When the emergency blow-out preventer 302 is activated, first a cuttingaction is achieved by activating the cutter 320. The cutting wheel 344is moved from its radially retracted position to its cutting positionwherein the cutting wheel touches the unexpanded tubular section 8 (FIG.7B). Subsequently, the cutting wheel cuts the unexpanded tubular section8, for instance by rotating around the tubular section 8 once, twice oras many times as required to sever a detached unexpanded section 350.During cutting, the ram blocks 326 remain in their retracted position(FIG. 7C).

After cutting, the detached unexpanded section 350 is lifted to create aspace for the respective ram type preventers (FIG. 8A). Lifting can forinstance be achieved by draw works or other lifting means (not shown)incorporated in the drilling rig.

In a subsequent step, one of the ram type preventers can be activated toseal the drilling annulus 32 (FIG. 8C). Typically, the operator willfirst activate either one of the pipe ram 322 or the annular preventer330, both of which will maintain the drill string 20. Otherwise, theshear ram 324 can be activated, wherein the ram blocks 328 will shearthe drill string 20, engage each other and seal the wellbore.

When the wellbore is closed, drilling fluid, having a predetermineddensity and weight, can be circulated via the drill string 20, theannulus 32 and through the kill line 334, as indicated by the arrows336, 338 and 352, until regaining control of the wellbore.

In a practical embodiment, the diameter and/or wall thickness of theliner 4 can be selected such that the expanded liner section 10 ispressed against the wellbore wall 14 during the expansion process. Theexpanded liner 10 may thus seal against the wellbore wall and/orstabilize the wellbore wall.

The wall thickness of the liner 4 may be equal to or thicker than about2 mm (0.08 inch). The wall of the liner 4 may be for instance more than2.5 mm thick, for instance about 3 to 30 mm thick or about 3.2 to 10 mm.The outer diameter of the unexpanded section may be larger than 50 mm (2inch), for instance in the range of about 50 to 400 mm (16 inch). Theexpanded section may have any outer diameter suitable for or commonlyused in hydrocarbon production. Additionally, the wall of the liner maycomprise a relatively strong material, such as a metal or preferablysteel, or be made of solid metal or steel. Such steel may include lowcarbon steel, for instance comprising less than 0.3% carbon. Thus, theliner 4 can be designed to have adequate collapse strength to support awellbore wall and/or to withstand internal or external pressuresencountered when drilling for hydrocarbon reservoirs.

The length and hence the weight of the unexpanded liner section 8 willgradually increase during extension of the wellbore. Hence, the downwardforce exerted by the pushing device 50 can be gradually decreased incorrespondence with the increasing weight of unexpanded liner section 8.As said weight increases, the downward force eventually may need to bereplaced by an upward force to maintain the total force within apredetermined range. This may prevent buckling of liner section 8.

During drilling, the unexpanded liner section 8 proceeds into thewellbore while the drill string 20 also gradually proceeds into thewellbore 1. The unexpanded liner section 8 is moved downward atsubstantially the same speed as the drill string 20, so that the bendingzone 14 remains at a relatively short distance above the drill bit 22.Herein, said short distance indicates the so-called open hole section L1(see FIG. 1), i.e. the unlined section, of the wellbore 1. The method ofthe present invention enables an open hole section having a length L1smaller than, for instance, about 100 or smaller than 50 metres at alltimes while drilling the wellbore.

The unexpanded liner section 8 may be supported by the drill string 20,for example by means of a bearing device (not shown) connected to thedrill string, which supports the U-shaped lower section 12. In that casethe upward force is suitably applied to the drill string 20, and thentransmitted to the unexpanded liner section 8 through the bearingdevice. Furthermore, the weight of the unexpanded liner section 8 thencan be transferred to the drill string and utilised to provide a thrustforce to the drill bit 22.

Drilling fluid containing drill cuttings is discharged from the wellbore1 via outlet conduit 90. Alternatively, drilling fluid may be circulatedin reverse circulation mode wherein the drilling fluid is pumped intothe wellbore via the conduit 90 and discharged from the wellbore via thedrill string 20.

When it is required to retrieve the drill string 20 to surface, forexample when the drill bit 22 is to be replaced or when drilling of thewellbore 1 is complete, the reamer section 26 can be collapsed to itsradially retracted mode, wherein the radial diameter is smaller than theinternal diameter of the unexpanded liner section 8. Subsequently, thedrill string 20 can be retrieved through the unexpanded liner section 8to surface.

With the wellbore system of the invention, it is achieved that thewellbore is progressively lined with the everted liner directly abovethe drill bit, during the drilling process. As a result, there is only arelatively short open-hole section L1 of the wellbore during thedrilling process at all times. Advantages of a short open hole sectioninclude limited possibility of influx into the wellbore, which willminimize the resulting pressure increase and simplify well control. Theadvantages of such short open-hole section will be most pronouncedduring drilling into a hydrocarbon fluid containing layer of the earthformation. In view thereof, for many applications it will be sufficientif the process of liner eversion during drilling is applied only duringdrilling into the hydrocarbon fluid reservoir, while other sections ofthe wellbore are lined or cased in conventional manner. Alternatively,the process of liner eversion during drilling may be commenced atsurface or at a selected downhole location, depending on circumstances.

In view of the short open-hole section during drilling, there is asignificantly reduced risk that the wellbore fluid pressure gradientexceeds the fracture gradient of the rock formation, or that thewellbore fluid pressure gradient drops below the pore pressure gradientof the rock formation. Therefore, considerably longer intervals can bedrilled at a single nominal diameter than in a conventional drillingpractice wherein casings of stepwise decreasing diameter must be set atselected intervals.

Also, if the wellbore is drilled through a shale layer, such shortopen-hole section eliminates possible problems due to a heaving tendencyof the shale.

After the wellbore has been drilled to the desired depth and the drillstring has been removed from the wellbore, the length of unexpandedliner section that is still present in the wellbore can be left in thewellbore or it can be cut-off from the expanded liner section andretrieved to surface.

In case the length of unexpanded liner section is left in the wellbore,there are several options for completing the wellbore. These are, forexample, as outlined below.

A) A fluid, for example brine, is pumped into the blind annulus 44between the unexpanded and expanded liner sections so as to pressurisethe annulus and increase the collapse resistance of the expanded linersection 10. Optionally one or more holes are provided in the U-shapedlower section 12 to allow the pumped fluid to be circulated.B) A heavy fluid is pumped into the blind annulus 44 so as to supportthe expanded liner section 10 and increase its collapse resistance.C) Cement is pumped into the blind annulus 44 in order to create, afterhardening of the cement, a solid body between the unexpanded linersection 8 and the expanded liner section 10. The cement may expand uponhardening.D) The unexpanded liner section is radially expanded (i.e. clad) againstthe expanded liner section, for example by pumping, pushing or pullingan expander through the unexpanded liner section.

In the above examples, expansion of the liner is started at surface orat a downhole location. In case of an offshore wellbore wherein anoffshore platform is positioned above the wellbore, it may beadvantageous to start the expansion process at the offshore platform, ator above the water surface. Herein, the bending zone moves from theoffshore platform to the seabed and subsequently into the wellbore.Thus, the resulting expanded tubular element not only forms a liner inthe wellbore, but also a riser extending from the offshore platform tothe seabed. The need for a separate riser is thereby obviated.

Furthermore, conduits such as electric wires or optical fibres forcommunication with downhole equipment can be extended in the annulusbetween the expanded and unexpanded sections. Such conduits can beattached to the outer surface of the tubular element before expansionthereof. Also, the expanded and unexpanded liner sections can be used aselectricity conductors to transfer data and/or power downhole.

Since any length of unexpanded liner section that is still present inthe wellbore after completion of the eversion process, will be subjectedto less stringent loading conditions than the expanded liner section,such length of unexpanded liner section may have a smaller wallthickness, or may be of lower quality or steel grade, than the expandedliner section. For example, it may be made of pipe having a relativelylow yield strength or relatively low collapse rating.

Instead of leaving a length of unexpanded liner section in the wellboreafter the expansion process, the entire liner can be expanded with themethod described above so that no unexpanded liner section remains inthe wellbore. In such case, an elongate member, for example a pipestring, can be used to exert the necessary downward force to theunexpanded liner section during the last phase of the expansion process.

In order to reduce friction forces between the unexpanded and expandedliner sections during the expansion process, a friction reducing layer,such as a Teflon layer, may be applied between the unexpanded andexpanded liner sections. For example, a friction reducing coating can beapplied to the outer surface of the unexpanded section 8. The frictionreducing layer reduces the annular clearance between the unexpanded andexpanded sections, reducing tendency of the unexpanded section tobuckle. Instead of, or in addition to, the friction reducing layer,centralizing pads and/or rollers can be applied in the blind annulusbetween the unexpanded and expanded sections to reduce the friction andthe annular clearance.

Instead of expanding the expanded liner section against the wellborewall (as described), the expanded liner section can be expanded againstthe inner surface of another tubular element, e.g. casing or a liner,already present in the wellbore.

Although the embodiments of the invention have been described includinga top drive, the present invention is likewise suitable for use withalternative drilling systems. The latter may include for instance adownhole motor instead of a top drive. Said downhole motor is a drillingtool comprised in the drill string directly above the bit. Activated bypressurized drilling fluid, it causes the bit to turn while the drillstring remains fixed. Examples of the downhole motor include apositive-displacement motor and a downhole turbine motor.

The present invention is likewise suitable for directional drilling,i.e. drilling wherein the drilling direction can be adjusted. Forinstance, a downhole motor may be used as a deflection tool indirectional drilling, where it is made up between the bit and a bentsub, or the housing of the motor itself may be bent.

The present invention is not limited to the above-described embodimentsthereof, wherein various modifications are conceivable within the scopeof the appended claims. For instance, features of respective embodimentsmay be combined.

1. A system for lining a wellbore, the system comprising: a drill stringfor drilling the wellbore; an expandable tubular element enclosing thedrill string, wherein a lower end portion of a wall of the expandabletubular element is bent radially outward and in axially reversedirection to define an expanded tubular section extending around anunexpanded tubular section; a pushing device for pushing the unexpandedsection into the expanded tubular section; a blow-out preventer forclosing off the wellbore in case of an emergency, wherein the blow-outpreventer encloses the unexpanded tubular section and comprises: acutter for cutting the unexpanded tubular section; and at least oneclosure device for closing the wellbore.
 2. The system of claim 1,comprising a wellhead device for closing an annular space between theunexpanded section and the expended section, wherein the blow-outpreventer is connected to said wellhead device.
 3. The system of claim1, wherein the closure device comprises one or more of: a shear ramdevice, a pipe ram device, an annular preventer device.
 4. The system ofclaim 1, wherein the cutter is arranged below the closure device.
 5. Thesystem of claim 1, wherein the blow-out preventer comprises a housing,which comprises at least one seal for sealing the housing with respectto the unexpanded tubular section, the at least one seal being arrangedbelow the cutter.
 6. The system of claim 1, wherein the cuttercomprises: a cutting wheel; and a guiding ring for guiding the cuttingwheel around the unexpanded tubular section.
 7. The system of claim 1,wherein the cutter comprises a laser cutter for cutting the unexpandedtubular section.
 8. The system of claim 1, wherein the expandabletubular element comprises a plurality of interconnected tubularsections.
 9. The system of claim 1, wherein the expandable tubularelement is provided with a longitudinal weld.
 10. Blow-out preventer fora system for lining a wellbore using an expandable tubular element,wherein a lower end portion of a wall of the expandable tubular elementis bent radially outward and in axially reverse direction to define anexpanded tubular section extending around an unexpanded tubular section,the blow-out preventer comprising: a housing for enclosing theunexpanded tubular section of the expandable tubular element; a cutter,which is arranged in the housing, for cutting the unexpanded tubularsection; and at least one closure device for closing an annulus betweena drill string and the unexpanded tubular section.
 11. Method for lininga wellbore using the system of claim 1.